It has long been known in the art to sterilize, for example, packages and packaging material webs with the aid of accelerated, energy-enriched electrons with which the webs or the packages are bombarded. The electron beam requisite for the sterilization is generated by means of a so-called electron accelerator which basically consists of a closed vacuum chamber which houses a cathode. From the cathode, electrons can be emitted in different ways and these are accelerated towards an anode which has high electric potential difference as compared with the cathode. The generated electrons accelerated toward the anode depart from the electron accelerator through a so-called window which in general includes a thin metal foil and is aimed at the object intended for sterilization. Such a sterilization with the aid of energy-enriched electrons has proved to be highly efficient for neutralizing micro-organisms. Many drawbacks which are associated with chemical sterilization and thermal sterilization are avoided through electron sterilization. Particularly, damage to materials which are not resistant to the chemical agents and/or to heat is avoided through electron sterilization.
One drawback in the electron accelerators which are employed today is that the window foil often breaks, since it is subjected to extreme stresses, and replacement of window foil is generally a complicated and time-consuming operation, which involves considerable operational disruption and costs. The window foil is generally an extremely thin aluminium foil, or titanium foil and the stresses to which it is exposed are, on the one hand, the mechanical stress which has its basis in the pressure difference between the vacuum chamber and the ambient environment surrounding the vacuum chamber, and, on the other hand, the fact that the electron beam through the foil entails a heating of the foil. Since the thin window foil makes up a part of the wall of the vacuum chamber, it must mostly be supported by some form of grid or mesh in order that the mechanical stresses arising out of the pressure difference do not become too great, and this grid or mesh may also be designed so that it leads off generated heat. When such electron accelerators are employed in connection with automatic packaging machines, they are most often disposed within a sterile chamber in which a sterile atmosphere must prevail in order to prevent the web which is sterilized by electron radiation from being reinfected after the sterilization operation. In order to achieve this sterile environment, the machine (and in particular the aseptic chamber) is initially sterilized with the aid of chemical sterilization agents, normally H.sub.2 O.sub.2, and steam. The atmosphere of a chemical sterilization agent such as H.sub.2 O.sub.2 is powerfully oxidizing, which entails that the window foil of the electron accelerator is chemically modified and weakened, especially when the chemical action is reinforced by heating by steam. The condensate which is formed when the steam changes aggregation state has also proved to have negative effects on the window foil and creates corroded areas in particular along the edge regions of the window foil. A further factor which acts negatively on the service life of the window foil is the ozone which is formed by the prevailing electric fields of high field force. Initial sterilization of the packaging machine must be carried out on each start-up after lengthy down time and the active life of the chemical sterilization agent or the steam is relatively lengthy (10 minutes to a few hours). Because of the chemical action on the outside of the window foil, the window foil is weakened in such a manner that the prevailing pressure difference on either side of the window foil in combination with the heating which takes place in the operative state of the electron accelerator and the action of the ozone created during operation often results in the window foil rupturing, whereupon the vacuum in the vacuum chamber of the electron accelerator is cancelled and the electron accelerator ceases to function. The window foil must, in such an event, be replaced, which, as was mentioned above, is an operation requiring considerable work and considerable time.